... so we don't have to export gosym.PCValue.

Change-Id: Ie8f196d5e5ab63e3e69d1d7b4bfbbf32b7b5e4f5
Reviewed-on: https://go-review.googlesource.com/33791
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>